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airboat with 3w70

Old 06-09-2013, 10:59 AM
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WhiteRook
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Default airboat with 3w70

what size airboat could i power with a 3w70 ? it will pull a 50 pound aircraft
Old 06-09-2013, 12:00 PM
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crispyspa
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Default RE: airboat with 3w70

[X(]

Well...since the engine will never really unload like it would if it were on a plane, you could run a 22" 3 blade prop to keep the CG down low. The boat will need to be just a tad wider than the diameter of the prop....say, 26- 30 wide and 39 - 53 long using 175% length to width ratio, You can adjust the ratio depending on how you want it to act in the water. A wider/ shorter boat will slide easier than a banking corner narrow/long boat. Mock it up in cardboard first to see if it's how you want it to look.

That will be a BIG boat if you decide to build it.
Old 06-09-2013, 12:03 PM
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WhiteRook
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Default RE: airboat with 3w70

it wont unload because of the resistance, from the water, right? how would you set the CG?
Old 06-09-2013, 12:18 PM
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Default RE: airboat with 3w70

Correct, that and no dive bombs.

The CG (center of gravity) is an imaginary point somewhere above the hull, but below the engine, center line, and ahead of the engine. A smaller prop just keeps it from being tippy, an inverted engine will also lower the CG. The CB (center of balance) is just that, the point at which the boat will balance if placed on a cylindrical object.

The CB is usually around 30% or 1/3 the length of the hull from the transom. A 30 inch hull would have a center of balance of about 10 inches from the stern.

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